The lone survivor of the Arizona wildfire that killed 19 firefighters was working as a lookout for the crew when conditions suddenly worsened and he narrowly escaped the inferno himself as he warned his colleagues to get out.

The "very distraught" survivor has been identified as Brendan McDonough, a member of the highly-trained Granite Mountain Hotshot Crew, according to the Prescott Fire Department.

McDonough, 21, was "acting as a lookout at the time for the crew," Prescott Fire Department spokesman Wade Ward told ABC News.

Ward said it is "very common" for crews to have a lookout at a higher location so that they can be in both radio and visual contact. He said that McDonough was on a hillside within a mile or two of the crew monitoring the situation.

When firefighters are involved in a situation, they have pre-determined "trigger points" that indicate to them that it is time to re-evaluate if the fire reaches the trigger points.

When conditions worsened, McDonough saw that his colleagues were in danger and warned them as his own trigger point was destroyed by the flames.

"He had radioed that his trigger point had been reached and so he radioed the crew and told them that he was leaving," Ward said. "As he was leaving, he had stated that the winds had changed so fast and picked up so fast that his trigger point was burned over within three minutes."

The elite team of firefighters was battling a raging wildfire in Yarnell, Ariz., when dry thunderstorms laced with strong, erratic winds shifted unexpectedly in the searing heat of the Southwest, likely creating the perfect storm that trapped and killed them, according to officials.

"He was warning them to get out," Ward said of McDonough. "They had made their plan to get out. They were attempting to reach their safety zone and get back to that point. He [McDonough] was picked up by a Blue Ridge Hotshot supervisor and was evacuated from the area and the crew attempted to get to their safety zone and they just couldn't outrun the fire. It changed that fast."

The wildfire killed 18 of 20 members of the Granite Mountain Hotshot Crew. The 19th dead firefighter was from another group. McDonough was the only survivor of Sunday's disaster.

Wade said that McDonough is "very distraught" and trying to figure out what happened.

"He's lost 19 of his best friends and co-workers and he's working through it the best that he can," Wade said. "He's being cared for not only by the Prescott Fire Department but the huge community around him and we're doing the best that we can to help him."

"It's not a good situation to not only be there, but to know that all of your buddies are gone," Wade said.

"He did exactly what he's supposed to do and the crew did exactly what they're supposed to do," he said. "There's nobody to blame. This is an accident."

The tragedy came at the start of the state's monsoon season, a weather phenomenon that brings lightning strikes, gusty winds, dust storms and sometimes rain to the state during the summer months.

Karen Takai, a fire information officer at Sandia Ranger district in New Mexico, said at a news conference today that the losses have been emotional for the firefighters who are still fighting the blaze but that they are determined to extinguish the fire for their fallen comrades.

"They were fighting the fire on the mountain. That was their charge. That was their job," Takai said. "To honor the firefighters, they're going to put this fire out."